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    <title>Sentinel Toolbox Help - Import AVHRR/3</title>
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<table class="header">
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        <td class="header">&nbsp; Import AVHRR/3</td>
        
    <td class="header" align="right"><a href="../general/overview/SnapOverview.html"><img src="../images/snap_header.jpg" border=0></a></td>
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<h3>Import AVHRR/3</h3>

<p>The NOAA AVHRR/3 reader enables the Sentinel Toolbox to import NOAA AVHRR/3 HRPT and AVHRR/3 LAC Level-1b data
    products.</p>

<p class="inote"><b>Note: </b>The AVHRR/3 reader is implemented in line with the "NOAA KLM User's
    Guide" (
    <object classid="java:org.netbeans.modules.javahelp.BrowserDisplayer">     
        <param name="content" value="https://www1.ncdc.noaa.gov/pub/data/satellite/publications/podguides/N-15%20thru%20N-19/pdf/0.0%20NOAA%20KLM%20Users%20Guide.pdf">
        <param name="text" value="<html><u>NOAA KLM User's Guide</u></html>">
    </object>) and
    is capable of reading data products in version v2 to v4.</p>

<p class="inote"><b>Note: </b>
    A good source for AVHRR/3 data products is 
    <object classid="java:org.netbeans.modules.javahelp.BrowserDisplayer">     
        <param name="content" value="https://www.bou.class.noaa.gov/saa/products/welcome">
        <param name="text" value="<html><u>CLASS NOAA</u></html>">
    </object>
</p>

<h4>Data Calibration</h4>

<p>While AVHRR pixel data is read into memory it is calibrated on the fly. Scan lines with
    calibration errors are detected and corresponding sample values are set to a special no-data-value.
    The Sentinel Toolbox will exclude those no-data-values from pixels statistics and displays them in a separate
    image overlay.</p>

<h4>Features</h4>

<p>The AVHRR/3 reader supports data products from the NOAA -15, -16, -17, and -18, as well as from
    the NOAA-N' satellites. The following features characterize the reader:</p>
<ul>
    <li>autodetection of the existence of an Archive Retrieval System (ARS) Header Record.</li>
    <li>autodetection of products in 8 bit, 10 bit and 16 bit format, as long as they contain all 5
        AVHRR bands.</li>
    <li>autodetection whether band 3a or band 3b or both are present in a single scene.</li>
    <li>reading of products which contain AVHRR/3 Local Area Coverage (LAC) and High Resolution
        Picture Transmission (HRPT) data sets.</li>
    <li>reading extensive Metadata from the header record.</li>
    <li>calibrating the raw values by applying calibration coefficients contained in the metadata.</li>
    <li>reading different quality flags.</li>
    <li>setting the no data value, if either the data or the calibration coefficients are invalid.</li>
    <li>geolocating the data products according to the given navigation data (solar zenith angle,
        satellite zenith angle, relative azimuth angle, latitude, longitude).</li>
    <li>setting the start and end date of the data acquisition.</li>
</ul>

<p>
    <!--From Format version 4, which is produced since 25 January 2006 (see
            <object classid="java:org.netbeans.modules.javahelp.BrowserDisplayer">     
                <param name="content" value="http://www.osdpd.noaa.gov/PSB/PPP/notices/notice_files/jan2506.html">
                <param name="text" value="<html><u>http://www.osdpd.noaa.gov/PSB/PPP/notices/notice_files/jan2506.html</u></html>">
            </object>),-->
    The products contain the CLAVR-x&nbsp; (<u><b>Cl</b></u>ouds from <u><b>AV</b></u>HR<b><u>R</u></b>
    E<b><u>x</u></b>tended cloud mask) cloud band. A draft of the CLAVR-x cloud mask
    theoretical basis document can be found at
    <object classid="java:org.netbeans.modules.javahelp.BrowserDisplayer">     
        <param name="content" value="http://cimss.ssec.wisc.edu/clavrx/clavrx_docs.html">
        <param name="text" value="<html><u>http://cimss.ssec.wisc.edu/clavrx/clavrx_docs.html</u></html>">
    </object>
    .<br>
</p>

<p>The reader has been tested with products obtained from the NOAA CLASS server which conforms to
    the format version 2 used for the NOAA -15, -16 and -17 satellites. Recently, NOAA has changed to
    the new version 3 format. The AVHRR/3 reader for the Sentinel Toolbox already supports both existing 10-bit packed
    format versions. AVHRR/3 data products can optionally have an Archive Retrieval System (ARS) Header
    Record. If this header is present, it is automatically detected by the reader. In particular, the
    AVHRR/3 reader implementation has the following features:</p>
<ol>
    <li>Read geometry data at tie-points.</li>
    <li>Provide geometry data at pixels using interpolation.</li>
    <li>Read raw counts and calibrate them to geo-physical values for all spectral channels.</li>
    <li>Channel 3a/3b usage detection.</li>
</ol>

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